Animal group size variation in a minimal attraction-repulsion agent-based model

bioRxiv (Cold Spring Harbor Laboratory)

Abstract

Abstract Grouping behaviour of prey animals is thought to be mainly driven by fear of predation and resource scarcity. Fear of predation often leads to small inter-individual distances, while resource scarcity leads to the opposite. Consequently, it is believed that the number of individuals in a group (group size) is an emergent property of the trade-off between acquiring scarce resources and preventing predation. We analysed whether group size can be reliably used as a proxy for this trade-off, using a deterministic attraction-repulsion agent-based model in a homogeneous area. In our model, each individual experiences distancedependent attraction and repulsion to all others in the area, where varying degrees of grouping behaviour emerge from the number and distance of intersections between the attraction and repulsion functions. We show that the coefficient of variation of group size generally lies between 50 and 150%, depending on both animal density and the trade-off between resource scarcity and predation. Given that the variations of group size are already this large in homogeneous and deterministic scenarios, we urge researchers to be cautious in using group size as a proxy for the resources/predation trade-off and consider inter-individual distance as a more direct and potentially more reliable alternative.

Authors 4

1. Jasper A.J. Eikelboom corresponding

   Wageningen University & Research

   Affiliation as printed

   Wageningen University and Research;

   Wildlife Ecology and Conservation Group, Wageningen University and Research, Droevendaalsesteeg 3a, 6708 PB Wageningen, Netherlands

   Wageningen University and Research

2. Arjen Doelman Aachen Mathematical Institute

   Leiden University

   Affiliation as printed

   Leiden University

   Mathematical Institute, Leiden University, P.O. Box 9512, 2300 RA Leiden, Netherlands

3. Frank van Langevelde

   Wageningen University & Research · University of KwaZulu-Natal

   Affiliation as printed

   School of Life Sciences, Westville Campus, University of KwaZulu-Natal, Durban 4000, South Africa

   Wageningen University and Research;

   Wildlife Ecology and Conservation Group, Wageningen University and Research, Droevendaalsesteeg 3a, 6708 PB Wageningen, Netherlands

   Wageningen University and Research

4. Henrik J. de Knegt

   Wageningen University & Research

   Affiliation as printed

   Wageningen University and Research;

   Wildlife Ecology and Conservation Group, Wageningen University and Research, Droevendaalsesteeg 3a, 6708 PB Wageningen, Netherlands

   Wageningen University and Research